Orin Kerr has this helpful and timely post at The Volokh Conspiracy. In addition to the roadblock cases he discusses, one might also consider the relevance of the Supreme Court's decision in Brigham City v. Stuart for the proposition that even a home entry might be permitted on less than probable cause in an appropriate emergency. That case involved entry where there were reasonable grounds, apparently short of probable cause, to believe that an occupant was in need of assistance. Given the possibility that a fugitive would take a hostage, police could not rely on a resident's assurance that no one in the home was in peril. Moreover, if the fugitive was reasonably believe to pose a substantial danger to many people, the Court might well not cabin Stuart to danger to those inside the residence entered.